The calculation 337.5 divided by Ks reading yields the base curve in which unit?

The calculation 337.5 divided by Ks reading yields the base curve in which unit?

• A. Millimeters
• B. Diopters
• C. Nanometers
• D. Cubic millimeters

Answer: (A)

The concept here is converting a keratometry reading into the lens’s back-surface radius. Ks is a corneal curvature measurement reported in diopters, and the base curve of a contact lens is the radius of its back surface, measured in millimeters. The standard conversion uses the constant 337.5, so base curve (mm) = 337.5 ÷ Ks (D). This yields a length in millimeters, which is exactly what the base curve represents. For example, a Ks of 40 D gives a base curve of about 8.44 mm, which aligns with typical lens radii. The result isn’t in diopters, nanometers, or cubic millimeters because those units don’t describe a radius length.

The concept here is converting a keratometry reading into the lens’s back-surface radius. Ks is a corneal curvature measurement reported in diopters, and the base curve of a contact lens is the radius of its back surface, measured in millimeters. The standard conversion uses the constant 337.5, so base curve (mm) = 337.5 ÷ Ks (D). This yields a length in millimeters, which is exactly what the base curve represents. For example, a Ks of 40 D gives a base curve of about 8.44 mm, which aligns with typical lens radii. The result isn’t in diopters, nanometers, or cubic millimeters because those units don’t describe a radius length.